Preparation of thioaniline



, phenylsulfide with iron.

Patented Sept. 28, 1943 Pent fde Nemours & Company, Wilmington, Del., a corporation of Delaware I No Drawing.

Application January 13, 1942, Serial No. 426,647

6 Claims. (01. 260-580) This invention relates to the preparation of thioaniline by the catalytic reduction of aminonitro'-diphenylsulfide.

The standard method for making thioaniline involves the reduction of 4-amino-4'-nitro-di- In thatprocess there is produced, along with the thioaniline, a-large amount of iron oxide. The thioaniline is comparatively non-volatile andis relatively insoluble in water so that it cannot easily be separated from the iron and iron oxide. Among the various methods which have been tried, some of which attained a certain measure of success and others of which were unsuccessful, are steam distillation, which proved impossible; solution in organic solvents, which is expensive and particularly difiicult because of the slimy nature of the iron o ide suspension; solution in dilute sulfuric acid which is impractical because of the low solubility of the sulfate in water, which requires great volumes; and extraction with hydrochloric acid, filtration, and precipitation by sodium sulfate. The last is the best of the known methods but has the objection that it is difficult to wash the iron salts out of the sulfate cake, which requires much time and a large amount of sodium sulfate solution.

The object of this invention is to prepare thioaniline by a simple and effective method. Other objects of the invention will be in part apparent and in part hereinafter set forth.

Although it would have been thought that the sulfur in the amino-nitro'-diphenylsulfide would poison a reducing catalyst,- it is my surprising discovery that thioaniline can be made by the catalytic reduction of amino-intro-diphenylsulfide with hydrogen. The reduction is carried out satisfactorily in methanol as a solvent but other solvents can be used. In the process the diphenylsulfide is put in a pressure chamber with the solvent, a reducing nickel catalyst and hydrogen. The mixture is heated under pressure for a period of time suflicient to complete the reduction. The solids in the reaction mass are removed by filtration, the solvent is recovered by distillation and the thioaniline is isolated by drowning in water. The thioaniline so produced is satisfactory for use in azocolors.

The following example illustrates but does not amino-4'-nitro-diphenylsulfide), which as a dry product had a setting point by maximum rise of 137 C., was charged to an autoclave with 1200 batches.

parts of methanol, 11 parts of reduced nickel catalyst supported on diatomaceous earth and 6 parts of ground limestone. The air in the autoclave was replaced by hydrogen and the temperature raised to C. The hydrogen pressure was raised to 500 lbs. At about C. reduction began and was complete in three hours, during which time the temperature rose to C. The

autoclave was cooled below the boiling point of methanol, the charge removed and filtered to remove the catalyst and limestone. Methanol was recovered by distillation up to 75 C. in the vapor stream without the use of a column, 840 parts of 95% methanol being thus recovered. This was satisfactory for reuse in subsequent The still residue was poured into cold water and a light gray, granular mass was obtained. This was filtered off and dried. The dry weight was 303 parts of thio-aniline, which is a weight yield of 95% of theory. The product had a setting point of 104 C. This was tested and found to be satisfactory for the manufacture of azo dyes.

The temperature of reduction may vary quite widely without injury to the product. In carrying out the reaction on a large scale the reduction has taken place mainly at to C., but that temperature is merely a desirable range, not a limitation.

Other reduction catalysts than reduced nickel may be used but reduced nickel is the common catalyst for hydrogen reductions and is at least as satisfactory as the others. Ethanol, isopropyl alcohol and toluene are satisfactory as solvents and illustrate the utility of organic solvents in general. The reduction can be carried out in water but proceeds slowly. For example 500 g. of nitro compound, 1400; cc. of water, 25 g. of catalyst and 3 g. of sodium acetate crystals were heated for 12 hours at 130-135 C. under pressure. A 20% conversion of the nitro body was obtained.

The final product can be isolated as a sulfate by dissolving it in hydrochloric acid and precipitating by the addition of sodium sulfate.

This process produces thioaniline at low cost and with efliciency of labor and materials.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1.. The process of preparing thioaniline which about 80 to about 140 C. and a pressure of about 500 lbs. per square inch, removing. the catalyst and its carrier by filtration, removing the methanol by distillation, drowning the residue of the reaction mass in water and filtering off the thio aniline.

2. The process of preparing thi'oanilinejwhich comprises mixing amino-nitro'.-diphenylsulfide.

with a solvent and reducing; itiwithh-ydrogen and a nickel catalyst at a temperature around. 100 (3. a

and at superatmospheric pressure, separating the reaction mass from the catalyst and solvent, drowning it in water and filtering 01f the thioaniline;

I 3, The process of preparing thioaniline which 20 comprises mixing amino-nitro'-diphenylsulfide with a solvent and reducing it with hydrogen and a nickel catalyst at a temperature around 100 C. and at superatmospheric pressure, and isolating the thioaniline.

4. The process of preparing thioaniline which comprises mixing amino-nitro-dipheny1su1fide with asolvent and reducing it with hydrogen and a nickel catalyst.

5. The process of preparing thioaniline which comprises mixing amino-nitro'-diphenylsulflde with a solvent therefor, and reducing it with free hydrogen ancla reduction catalyst.

, 6. The process of preparing thioaniline which comprises heating to reaction temperature a mixtureof amino-nitro'-diphenylsulfide, an organic solvent, and a reducing catalyst in the presence of an atmosphere of hydrogen under pressure.

LEE 0. HOLT. 

